This Center Grant continues a set of interrelated multidisciplinary investigations into the fundamental psychophysical, physiological, and morphological aspects of auditory and vestibular dysfunction. One set of investigations is concerned with the perceptual consequences of cochlear and retrocochlear malfunctions in persons with hearing disorders. These psychophysical investigations include experiments designed to assess specific properties of impaired hearing and to relate those properties to deficits in speech perception. Another set of investigations, involving animal models, is concerned with the anatomical, physiological, and psychophysical correlates of well-defined experimentally induced inner ear damage and the mechanisms by which this damage affects auditory function. Finally, experiments are proposed on those disorders that also affect hearing. This project is a multidisciplinary and vestibular physiology, sensory psychology, audiology, and otolaryngology. The history of this program demonstrates both the financial efficiency and the scientific effectiveness of the Center-Grant concept. This collaborative program of research will continue to advance our understanding of the characteristics and mechanisms of hearing loss and vestibular dysfunction, and will have direct implications for clinical diagnosis and eventual management of disorders of hearing and vestibular function.